WO2007142313A1

WO2007142313A1 - Receiver and frequency information estimation method

Info

Publication number: WO2007142313A1
Application number: PCT/JP2007/061581
Authority: WO
Inventors: Yasuhiro Hamaguchi; Hideo Nanba; Shimpei To
Original assignee: Sharp Kabushiki Kaisha
Priority date: 2006-06-07
Filing date: 2007-06-07
Publication date: 2007-12-13
Also published as: CN101467372A; US20090196166A1; EP2028777A1; US8000224B2; JPWO2007142313A1; JP5042219B2

Abstract

[PROBLEMS] To suppress distortion of a calculated result of frequency response generated by removing a noise and the like when estimating a propagation path by the time-reversed spread propagation path estimation method. [MEANS FOR SOLVING PROBLEMS] A receiver (100) includes: a Fourier transform unit (105) for performing the Fourier transform on a propagation path estimation symbol containing a sub-carrier modulated by a known signal different for each of antennas and calculating first frequency information; a multiplication unit (107) for multiplying the first frequency information by a complex number conjugate signal of known signals so as to calculate second frequency information for each sub-carrier; an interpolation information generation unit (121) for selecting a part of information from the second frequency information according to the known signals and generating interpolation frequency information for interpolating sub-carriers by using the selected information; a sub-carrier interpolation unit (122) for interpolating the interpolation frequency information to the second frequency information so as to calculate third frequency information; and an inverse Fourier transform (109) for subjecting the third frequency information to the inverse Fourier transform.

Description

Specification

Receiver and frequency information estimation method

Technical field

[0001] The present invention performs propagation channel estimation by receiving multicarrier, in particular, Orthogonal Frequency Division Multiplexing (OFDM) symbols consecutively arranged on a predetermined number of predetermined subcarriers. The present invention relates to a multicarrier receiver and a receiving method.

Background art

[0002] In recent years, the number of users seeking higher speed to a wireless communication system has been increasing, and multicarrier transmission systems represented by OFDM have been attracting attention as one of the systems that can realize high speed and large capacity. There is. The OFDM scheme is a scheme in which several tens to several thousands of carriers are arranged in a frequency interval that theoretically causes no interference, and information signals are transmitted in parallel by frequency division multiplexing. The OFDM scheme has an advantage of being less susceptible to multipath interference since the symbol time becomes longer when the number of subcarriers used is increased compared to a single carrier scheme of the same transmission rate.

However, in a multipath environment, since each subcarrier is subjected to different amplitude fluctuation and phase fluctuation, it is necessary to compensate for these fluctuation when demodulating data on the receiving side. As a method of compensating for the propagation path, on the transmitting side, all or a part of the subcarriers are modulated with a known code between the transceivers and transmitted as a pilot signal, and on the receiving side, the received pilot signal strength There is a method of estimating received channel fluctuation and compensating the estimated channel fluctuation. Hereinafter, in the present specification, a multicarrier signal including this pi-port signal is referred to as a “channel estimation symbol”. Also, when the signal form is OFDM, it is called “propagation channel estimation OFDM symbol”.

[0004] Estimation of propagation path fluctuation 'In the compensation, Fourier transform or inverse Fourier transform is used, and noise or interference is eliminated using concentration of the delay profile signal in a certain range of the output of inverse Fourier transform. A time despreading channel estimation method can be adopted (Patent Document 1). The gain obtained by the time despreading channel estimation method is taken as the time despreading gain. OFDM In the system, the number of Fourier transform points (or the number of inverse Fourier transform points) used in the transmitting / receiving device and the signal to be transmitted are allocated (used for signal transmission) in order to cope with the formation of guard bands or filtering processing in the transmitter. Most of them agree that the number of subcarriers is the same. The number of Fourier transform points is usually 2 ⁿ .

Particularly when the number of Fourier transform points and the number of subcarriers are different, when the channel is estimated by the time despreading channel estimation method, although the time despreading gain can be obtained, the ratio of received signal power to noise power (SNR: Depending on the signal to noise power ratio, the adverse effect due to distortion was noticeable at the end of the frequency response estimation band. This distortion is more influential toward the end of the band for estimating the propagation path. For this reason, a technique is also disclosed that improves the time despreading channel estimation method.

For example, in Patent Document 1, frequency information (frequency information from which noise or the like has been removed) whose propagation path has been estimated by the time despreading propagation path estimation method is used for propagation path compensation in the central part of the band. A method is disclosed in which the propagation path of subcarriers located at is used for propagation path compensation before removing noise and the like. Patent Document 2 discloses a technique for facilitating the determination of a reference element related to noise generated in a transmission channel. That is, as a technique for determining a reference element relating to noise, it is disclosed that a threshold is set upon reception, transmission is performed by increasing the power of the reference element, or a combination of these. That is, by utilizing the fact that the delay profile signal is concentrated in a certain range of the inverse Fourier transform output, noise and interference can be removed, and when removing noise power from the delay profile, signal power components can also be removed. It is intended to prevent the occurrence of distortion caused by According to this method, it is possible to calculate the frequency response with high accuracy by the time despreading gain without being affected by distortion.

[0007] Also, in recent years, MIMO (Multi_Input Multi-Output) technology has been actively studied. This technology transmits different data streams from two or more different antennas, identifies it at the receiver, and demodulates the data, which contributes significantly to the improvement of the transmission rate. A MIMO-OFDM system, which is OFDM using MIMO technology, is also being considered, in which the propagation paths between the transceivers can be estimated efficiently and accurately. It is an important issue.

[0008] Non-Patent Document 1 shows a channel estimation method using CI (Carrier Interferometry) (hereinafter referred to as "CI method"), and the feature of the present technology is that one channel estimation OFDM scheme is used. It is possible to estimate the propagation path from a plurality of transmitting antennas with a symbol. In the CI method, signals transmitted from each antenna can be distinguished by changing the phase rotation amount of one propagation path estimation signal and using different propagation path estimation signals in each antenna. Therefore, for example, when using antenna 1 and antenna 2, when calculating the propagation path from antenna 1, the frequency conversion is performed by removing the pulse corresponding to the signal power from antenna 2. It is possible to calculate the frequency response from one. Similarly, when the propagation path from the antenna 2 is calculated, the frequency response from the antenna 2 can be calculated by removing the pulse corresponding to the signal power from the antenna 1 and performing frequency conversion.

Patent Document 1: Japanese Patent Application Publication No. 2005-130485

Patent Document 2: Patent No. 3044899

Non-Patent Document 1: Kazunari Yokomakura et al., "A Study on Channel Estimation Method using Carrier Interferometry in MIMO-OFDM System," IEICE Technical Report, RCS 2005- 79, August 2005, p. 91 — 96

Disclosure of the invention

Problem that invention tries to solve

However, even when a channel estimation OFDM symbol multiplexed by CI method is used in a MIMO-OFDM system, a channel despreading channel estimation method is used as in the case of one transmit antenna. In the estimation of the distortion, the problem of distortion occurs because the number of Fourier transform points and the number of subcarriers do not match. Further, in the MIMO-OFDM system, the frequency response is a waveform obtained by receiving channel estimation symbols transmitted from a plurality of antennas, and therefore, as in the method disclosed in Patent Document 1, the subcarrier It is not possible to use the frequency response result used for propagation path compensation by position

[0010] The present invention has been made in view of such circumstances, and uses a plurality of antennas to perform recording. In a system for transmitting and receiving multi-carrier symbols, a receiver and frequency information estimation method for suppressing distortion of a calculation result of frequency response caused by removing noise etc. when estimating a propagation path by the time despreading channel estimation method Intended to be provided. Means to solve the problem

(1) A receiver according to the present invention receives subcarriers for propagation path estimation transmitted from a plurality of transmission antennas, including subcarriers modulated with different known signals, and receives from each of the transmission antennas Receiver for estimating the propagation path of the channel, the Fourier transform unit calculating the first frequency information for each subcarrier by Fourier-transforming the received channel estimation symbol, and the propagation path estimation symbol A signal generation unit that generates a known signal used to modulate subcarriers included in the signal; a division unit that divides the first frequency information by one of the known signals to calculate second frequency information; Calculating an information of frequency response from the transmitting antenna at a position where no subcarrier is transmitted from the first frequency information or the second frequency information; interpolating the third frequency information; And the third frequency Characterized in that it comprises an inverse Fourier transform unit for inverse Fourier transform to multi-address, the.

As described above, according to the receiver of the present invention, when the propagation path estimation symbol received from each of the plurality of antennas is received and the propagation path is estimated, based on the characteristic of the known signal. , Calculate information of frequency response from the transmitting antenna at a position where no subcarrier is transmitted. Channel estimation symbols are received at the receiver as symbols contained in multicarrier symbols. Also, propagation path estimation symbols include subcarriers modulated with known signals that are different for each transmit antenna at the transmitter side. The known signal used for modulation at the transmitter side is also known in advance by the receiver. Therefore, based on the characteristics of the known signal, the receiver selects a subcarrier suitable for interpolation from the subcarriers in the signal band, and uses the first or second frequency information of the selected subcarrier as interpolation frequency information. Can be calculated. As a result, since it is possible to estimate the propagation path by the time despreading propagation path estimation method using the frequency response at a frequency wider than the frequency band actually transmitted, it is possible to reduce distortion occurring at the end of the band. Become.

(2) In the receiver according to the present invention, the extrapolation unit is a known signal obtained by modulating subcarriers at the same position of propagation path estimation symbols transmitted from the plurality of antennas. The present invention is characterized by including an interpolation information generation unit that selects subcarriers based on the combination and generates frequency information to be interpolated using frequency information of the selected subcarriers.

As described above, when the receiver receives a multicarrier symbol modulated with known signals of different values by each of the plurality of antennas, the outer ring unit transmits the plurality of antennas per subcarrier. The relationship between subcarriers is determined based on a combination of different known signals for each, and frequency information is selected based on the determined result. That is, the above-mentioned outer band part forms a plurality of signal bands based on the characteristics of known signals of different values for each antenna (combination of known signals of the same subcarrier number obtained by modulating the subcarriers of each antenna). A part or all of the sub-carriers are selected from the sub-carriers, and frequency information to be interpolated is generated based on the selected sub-carrier frequency information. As a result, since it is possible to estimate the propagation path by the time despreading propagation path estimation method using the frequency response at a frequency wider than the frequency band actually transmitted, it is possible to reduce distortion occurring at the end of the band. Become.

(3) Further, in the receiver according to the present invention, the interpolation information generation unit is characterized by selecting a subcarrier in which a matrix generated by a different known signal is regular for each of the plurality of antennas. I assume.

Thus, when a subcarrier whose matrix generated by a known signal is regular is selected, if the frequency characteristic at the selected subcarrier position hardly changes, the interpolation information generation unit It is possible to calculate the frequency response from each antenna. Then, by extrapolating out of the band using the calculated value, the propagation path can be estimated by the time despreading channel estimation method using the frequency response at a frequency wider than the actually transmitted frequency band. It is possible to reduce distortion that occurs on the end side of the

(4) The receiver according to the present invention includes subcarriers modulated with different known signals generated by providing different amounts of phase rotation 毎 for each transmitting antenna between elements of a predetermined code. A receiver for receiving propagation path estimation symbols transmitted from a plurality of transmission antennas and estimating the propagation paths from the transmission antennas, the received propagation path estimation symbols being subjected to Fourier transform to generate A Fourier transform unit that calculates first frequency information for each carrier, and a known one used to modulate subcarriers included in a propagation path estimation symbol. The phase rotation amount from the signal generation unit that generates a signal, the division unit that divides the first frequency information by one of the known signals to calculate second frequency information, and the second frequency information Calculating and interpolating information on the synthesized frequency response at a position where no subcarrier is transmitted based on Θ, and performing an inverse Fourier transformation on the third frequency information and an outer portion generating the third frequency information And inverse Fourier transform unit.

[0018] As described above, when the different known signals use one known signal and the phase rotation amount Θ given to each subcarrier is made a different known signal by making the values different for each transmitting antenna, The outer portion selects a part of information based on the relationship of the phase difference given to the subcarriers of the same subcarrier number caused by a plurality of different phase rotation amounts set for each of the transmitting antennas. The carrier can be selected, and the second frequency information of the selected subcarrier can be used to generate / exclude appropriate frequency information. As a result, since the propagation path can be estimated by the time despreading propagation path estimation method using the frequency response at a frequency wider than the frequency band actually transmitted, it is possible to reduce the distortion generated at the end of the band.

(5) In the receiver according to the present invention, the outer ring section calculates a difference すべて for all two different Θ, selects a subcarrier based on Θ, and selects the selected subcarrier of

diff diff

It is characterized by having an interpolation information generation unit that generates frequency information to be interpolated using frequency information.

[0020] Thus, based on the difference Θ calculated for all two different moths,

diff

Since the frequency information of the selected subcarrier is used to generate frequency information to be interpolated, appropriate frequency information can be generated and extrapolated. As a result, since the propagation path can be estimated by the time despreading channel estimation method using the frequency response at a frequency wider than the frequency band actually transmitted, it is possible to reduce the distortion generated at the end of the band.

(6) Further, in the receiver according to the present invention, the interpolation information generation unit may set m XI θ I = 2η π (m, n is a natural number) for each of the phase rotation amount differences Θ Θ 満 diff diff

If Lm_A (LCM_A is an integer) is calculated as LCM_A (LCM_A is an integer), the least common multiple of LCM A is calculated starting from the subcarrier to be interpolated. It is characterized in that frequency information is selected from subcarriers arranged at a distance from each other.

[0022] As described above, since the interpolation information generation unit performs the extrapolation, the propagation path can be estimated by the time despreading propagation path estimation method using the frequency response at a frequency wider than the frequency band actually transmitted. It is possible to reduce distortion that occurs at the end of the band.

[0023] (7) In the receiver according to the present invention, the mantle has all the phase rotation amounts Θ.

In the case of integer multiples of 0 g, calculate LCM_B (LCM_B is an integer) as the smallest m that satisfies m XI 0 g I = 2ηπ (m, n is a natural number and | θ | is an absolute value of Θ). The present invention is characterized in that frequency information is selected from subcarriers placed apart from the least common multiple LCM_B starting from the subcarrier to be interpolated.

As described above, it is possible to select a subcarrier for calculating interpolation frequency information based on the relationship between the plurality of known signals. This makes it possible to select appropriate frequency information based on the mutual relationship of known signals, and propagates by the time despreading channel estimation method using the frequency response at a frequency wider than the actually transmitted frequency band. Since the path can be estimated, it is possible to reduce distortion occurring at the end of the band.

(8) The receiver according to the present invention is characterized in that the interpolation information generation unit selects frequency information of a subcarrier close to a subcarrier to be interpolated.

Thus, interpolation is performed based on frequency information of subcarriers close to propagation path characteristics by selecting frequency information of subcarriers close to the subcarrier to be interpolated in addition to the interrelation of the plurality of known signals. Frequency information can be calculated. This can further reduce distortion.

(9) A frequency information estimation method according to the present invention includes subcarriers each modulated by different known signals, receives a propagation path estimation symbol transmitted from a plurality of transmission antennas, and transmits each transmission antenna. A method of estimating frequency information to be used for estimation of a propagation channel from the frequency domain, comprising Fourier-transforming the received channel estimation symbol to calculate first frequency information for each subcarrier, and calculating the first frequency The second frequency information is calculated by dividing the information by one of known signals used for modulation of the subcarrier included in the propagation path estimation symbol, and the first frequency information or the second frequency information is calculated. Calculating the information of the frequency response from the transmitting antenna at a position where no subcarrier is transmitted, and interpolating the third frequency Number information is calculated, and the third frequency information is inverse Fourier transformed.

As described above, according to the receiver of the present invention, when the propagation path estimation symbol received from each of the plurality of antennas is received and the propagation path is estimated, based on the characteristics of the known signal. , Calculate information of frequency response from the transmitting antenna at a position where no subcarrier is transmitted. Channel estimation symbols are received at the receiver as symbols contained in multicarrier symbols. Also, propagation path estimation symbols include subcarriers modulated with known signals that are different for each transmit antenna at the transmitter side. The known signal used for modulation at the transmitter side is also known in advance by the receiver. Therefore, based on the characteristics of the known signal, the receiver selects a subcarrier suitable for interpolation from the subcarriers in the signal band, and uses the first or second frequency information of the selected subcarrier as interpolation frequency information. Can be calculated. As a result, since it is possible to estimate the propagation path by the time despreading propagation path estimation method using the frequency response at a frequency wider than the frequency band actually transmitted, it is possible to reduce distortion occurring at the end of the band. Become.

(10) In the frequency information estimation method according to the present invention, a subcarrier modulated with a different known signal generated by giving a different amount of phase rotation 毎 to each transmit antenna between each element of a predetermined code A channel information estimation method for receiving propagation path estimation symbols transmitted from a plurality of transmit antennas and used to estimate the propagation paths from each of the transmit antennas, the received propagation path estimation symbols Fourier transform is performed to calculate first frequency information for each subcarrier, and the first frequency information is divided by one of known signals used for modulation of subcarriers included in propagation path estimation symbols. Then, second frequency information is calculated, and from the second frequency information, information of frequency response synthesized at a position where the subcarrier is not transmitted is calculated based on the phase rotation amount 'interpolation Te, generating the third frequency information, characterized by inverse Fourier transforming the third frequency information.

[0030] As described above, when the different known signals use one known signal and the phase rotation amount Θ given to each subcarrier is made a different known signal by setting different values for each transmitting antenna, The outer ring portion is a phase given to subcarriers of the same subcarrier number generated by a plurality of different phase rotation amounts 設定 set for each of the transmission antennas. Subcarriers for selecting partial information can be selected based on the relationship of difference, and appropriate frequency information can be generated and extrapolated using the second frequency information of the selected subcarriers. As a result, since it is possible to estimate the propagation path by the time despreading propagation path estimation method using frequency response at a frequency wider than the frequency band actually transmitted, it is possible to reduce distortion occurring at the end of the band. Become.

Effect of the invention

According to the present invention, when receiving propagation path estimation symbols transmitted from different antennas and estimating the propagation path by the time despreading propagation path estimation method, the characteristics of different known signals are different for a plurality of antennas. By estimating the frequency information to be interpolated based on this, it is possible to suppress distortion of the calculation result of the frequency response that is generated by removing noise and the like.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, embodiments of the present invention will be described with reference to the drawings. Components and corresponding parts having the same configuration or function in the drawings are denoted by the same reference numerals, and the description thereof will be omitted. Each embodiment will be described using a MIMO-OFDM system. However, the present invention is not limited to the MIMO-OFDM system, and is also referred to as a pilot symbol for propagation path estimation (a pilot symbol), which is transmitted from a plurality of antennas and modulated with different known signals (known codes) for each antenna. The present invention can be applied to a receiver that receives a subcarrier to which known data is assigned in a pilot symbol as a pilot subcarrier) and a frequency information estimation method. Also, to simplify the description, it is assumed that two transmitter antennas are provided on the transmitter side, and the propagation path estimation OFDM symbol is simultaneously transmitted from these two transmission antennas (transmission antenna 1 and transmission antenna 2). . It is assumed that two different antennas are in the same transmitter. However, the present invention can be applied to a system in which propagation path estimation F FDM symbols are transmitted at almost the same timing even with antennas located at different transmitters (transmission devices) whose necessity is less. In each embodiment, the total number m of subcarriers used is 768, and the number of FFT points is 1024.

Further, in the following description, in the propagation path estimation OFDM symbol, it is assumed that all the subcarriers are modulated by the known signal between the transmitter and the receiver. Known message here The signal is composed of a plurality of elements (complex signals, which are often set to have an amplitude of 1 for simplicity), and each element modulates subcarriers in the channel estimation OFDM symbol. The OFDM signal generated from transmitting antenna 1 with known signal C (ck is a component of C, k is a positive integer less than or equal to the number of subcarriers, and indicates the subcarrier number) is an OFDM symbol for channel estimation. It shall be sent as. An OFDM signal generated from the transmitting antenna 2 with a known signal D (where dk is a component of D, k is a positive integer equal to or less than the number of subcarriers, and indicates a subcarrier number) is used as an OFDM symbol for channel estimation. It shall be sent. The known signal C and the known signal D may be written as a code C and a code D, respectively. The terms ck and dk are sometimes referred to as element ck, element dk, or component ck and component dk, respectively.

The known signal uses a different code for each antenna. For example, it is assumed that the known signal C and the known signal D described above are different. Also, in the CI method described in the second embodiment, a plurality of codes are generated by applying a different phase difference rotation between subcarriers for each antenna with respect to one known signal C. Such a code Is also called a different code.

[0035] In the present specification, Fourier transform includes Fast Fourier Transform (FFT) and Discrete Fourier Transform (DFT), and Inverse Fourier Transform includes Inverse Fast Fourier Transform (IFFT: Inverse). It is a concept including Fast Fourier Transform) and Inverse Direct Fourier Transform (IDFT). In the following description, although it demonstrates using a fast Fourier transform as a Fourier transform and an inverse fast Fourier transform as an inverse Fourier transform, it is possible to apply this invention also to a discrete Fourier transform and an inverse discrete Fourier transform. The following description will be made using fast Fourier transform and inverse fast Fourier transform, and the number of points to be Fourier transformed (the number of Fourier points) is FFT point, the number of points to be inverse Fourier transformed (the number of inverse Fourier points) is IFFT point Explain as a number. Also, the number indicated by the FFT point or IFFT point is the same as the subcarrier number.

Further, a band to be subjected to fast Fourier transform (inverse fast Fourier transform) processing is an FFT processing band (IFFT processing band), and a band to which a signal is allocated among the FFT processing bands is a signal band. Also for the FFT processing band power, the band excluding the signal band is a band that is a candidate for interpolation (cover). And the interpolation target band.

Furthermore, in the present invention, “time despreading channel estimation method” is used as a channel estimation method. This channel estimation method uses Fourier transform, inverse Fourier transform, and concentration of the delay profile signal to a certain range of the output of inverse Fourier transform in estimation of channel variation and compensation. “Time despreading gain” is a gain obtained by the time despreading channel estimation method. However, when removing noise and interference, an estimation error occurs at the end of the signal band, which is a problem especially when the channel quality is good. An object of the present invention is to reduce the influence of this distortion as much as possible, and more specifically, based on a code used in generating an OFDM signal for propagation path estimation, a frequency response at a position where a signal is not actually transmitted. The problem is to be solved by

In the first embodiment below, when using a channel estimation OFDM symbol with a signal having no relationship between codes used for transmission, in the second embodiment, a propagation path called a CI method is used. This is shown when using the estimation OFDM symbol.

First Embodiment

In the first embodiment, a channel estimation OFDM symbol modulated with known signals of different values is transmitted and received for each antenna. In the first embodiment, the known signal C and the known signal D have different values. In the present embodiment, the known signal C is a component ck (cl X e, c2 X e ^jei , c

3 X e ^{j 8} \, cm X e ^iei ), the known signal D is a component dk (dl x e ^{θ θ 2} , d 2 x e ^{θ θ} d 3

It is represented by X e ^{je 2} ,, dm X e ² ), ck, dk is ± 1, m is the total number of subcarriers, and j is an imaginary unit. Therefore, the channel estimation OFDM symbol is the same as in the case where each subcarrier is B PSK modulated.

FIG. 1 is a block diagram showing an example of the configuration of a receiver 100 according to the present invention. The receiver (multicarrier wireless receiver) 100 shown in FIG. 1 includes an antenna unit 101, a wireless reception unit 102, an A / D (Analog Z Digital) conversion unit 103, an OFDM symbol synchronization unit 104, and an FFT unit (Fourier conversion unit). And 105, a propagation path compensation unit 112, a decoding unit 113, and a propagation path estimation unit 201. The propagation path estimation unit 201 includes a pilot extraction unit 106, a multiplication unit 107, a pilot complex symbol combination signal generation unit 108, an IFFT unit (inverse Fourier transform unit) 109, a noise removal unit 110, an FFT unit 111, and an envelope. A unit 120 is provided. The signal received by the antenna unit 101 is first frequency-converted by the wireless reception unit 102 to a frequency band in which an analog signal can be converted into a digital signal. The A / D conversion unit 103 converts the frequency-converted signal into a digital signal. The OFDM symbol synchronization unit 104 performs OFDM symbol synchronization on the converted digital signal and removes a guard interval (GI: Guard Interval).

Thereafter, the FFT unit 105 performs Fourier transform on the digital signal from which GI has been removed, and separates the signal into subcarriers.

Next, the signal separated for each subcarrier is input to channel compensation section 112 and channel estimation section 201, and channel estimation section 201 carries out the following processing.

The pilot extraction unit 106 extracts a pilot subcarrier signal from the Fourier transformed OFDM symbol for channel estimation. In this embodiment, since all subcarriers are assumed to be pilot subcarrier signals in OFDM symbol for channel estimation, frequency information of all subcarriers is extracted. The extracted frequency information is multiplied by the complex conjugate signal of the pilot subcarrier signal generated by the pilot complex conjugate signal generator 108 used in the transmitter in the multiplier 107. The propagation path fluctuation in the frequency domain can be obtained as the amplitude value and the phase value of the propagation coefficient by the multiplication in the multiplication unit 107. This amplitude value and phase value are called frequency information or frequency response.

Although it is basically necessary to perform complex division with a code used for a pilot subcarrier signal in order to obtain frequency information, this embodiment and the embodiment described below are for reducing the amount of calculation. Let the amplitude of the code used for the pilot subcarrier signal be 1, and substitute the complex division with the multiplication of the complex conjugate signal to obtain the frequency response. The frequency response calculated by this complex division contains noise and interference in the frequency response of the propagation path.

Further, in the present specification, an input to the multiplication unit 107, that is, the signal extracted by the pilot extraction unit 106 after signal conversion by Fourier transform is used as the first frequency information. Also, the output from the multiplication unit 107, that is, the value obtained by multiplying the first frequency information by the complex conjugate signal is set as the second frequency information. [0047] With respect to the calculated second frequency information, extrapolation section 120 extrapolates the signal of the subcarrier in the interpolation candidate band to which no signal is assigned, and interpolates the frequency response. The output of the external 120 power, that is, the information obtained by extrapolating the second frequency information is used as the third frequency information. A detailed operation of the mantle 120 will be described later.

Next, IFFT section 109 performs inverse Fourier transform on the third frequency information, and changes propagation path fluctuation in the frequency domain into propagation path fluctuation (impulse response or delay profile) in the time domain. Convert. In general, in a signal of propagation path fluctuation in the time domain, the power is concentrated in a certain range of IFFT output, so the noise eliminator 110 regards signals other than the range in which the power is concentrated as noise and replaces it with zero. Do the processing.

The FFT unit 111 performs Fourier transform on the output of the noise removing unit 110, and thereby calculates frequency information of the OFDM signal band. This is because the noise removing unit 110 removes noise and interference from the second frequency information and the third frequency information which are obtained earlier, so that the frequency information becomes highly accurate. The frequency information output from the FFT unit 111 is used as frequency information for compensation. The propagation path compensation unit 112 performs propagation path compensation using the signal separated for each subcarrier output from the FFT unit 105 and the frequency information for compensation output from the FFT unit 111. The data thus subjected to propagation path compensation is subjected to decoding processing such as demodulation and error correction in the decoding unit 113 to obtain data. Data are sent to upper layers and so on.

Next, the process of the mantle portion 120 will be described. In FIG. 1, the extrapolation unit 120 is disposed between the pilot extraction unit 106 and the multiplication unit 107 only in the case of the first embodiment, which is disposed between the multiplication unit 107 and the IFFT unit 109. It is also possible. Further, since a MIMO system using two transmit antennas is assumed, the channel estimation unit 201 estimates channel information of each of the two antennas. Although not explicitly shown in FIG. 1, the power for preparing two propagation path estimation units 201 (the number of antennas), and the number of antennas looped around the propagation path estimation unit 201 enables a plurality of antennas to be prepared. Estimate the propagation path from Furthermore, although it is necessary for the channel compensation unit 112 and the decoding unit 113 to operate according to the MIMO reception, the contents are not affected by the present invention, so the description will be omitted.

As shown in FIG. 1, the envelope unit 120 includes an interpolation information generation unit 121, a subcarrier interpolation unit 122, and the like. Equipped with Interpolation information generation section 121 is configured based on a combination of different known signals used in generating a channel estimation OFDM symbol for each antenna from either the first frequency information or the second frequency information. , And select partial information, and use the selected information to generate interpolation frequency information to interpolate information in the signal band to which no signal is assigned. In particular, in the present embodiment, a combination of known signals obtained by modulating subcarriers at the same position (subcarrier number), a subcarrier to be a source of interpolation frequency information is selected, and first frequency information of the selected subcarrier is selected. Alternatively, the interpolation frequency information is generated using the second frequency information. The subcarrier interpolation unit 122 interpolates the interpolation frequency information generated by the interpolation information generation unit 121 into second frequency information to calculate third frequency information. Specifically, the subcarrier interpolation unit 122 adds the interpolation frequency information to the second frequency information.

Here, the details of the operation of the mantle portion 120 of the present embodiment will be shown. An example of an input waveform (second frequency information) to the mantle 120 (interpolation information generation unit 121) is shown in FIG. In FIG. 2, the horizontal axis is the FFT point, and the vertical axis is the power. The propagation path estimation unit 201 inputs propagation path estimation OFDM signals transmitted from two transmission antennas. In Figure 2, FFT points 385 to 639 are not used for filtering, and zero corresponds to DC (DC potential), so an example of an input waveform when not used in a normal OFDM system Is shown. Therefore, in Fig. 2, the system uses the 384 waves of FFT point force 384 and the sub-carriers corresponding to 384 waves of up to 640 power 1023 (FFT point repulsive force et al. 384 waves Although the system is configured with two signal bands of 384 waves up to 640 powers and 1023 in the frequency band where actual transmission is performed, the subcarriers are upper and lower frequencies centering on the subcarrier set to DC. Distributed).

The interpolation information generation unit 121 in the outer packet unit 120 estimates the frequency response of at least a part of the subcarrier of the interpolation target band in the guard band position where the FFT point is 385 to 639 unused FFT points. Then, the interpolation frequency information is generated, and the subcarrier interpolation unit 122 has a function of inserting into a subcarrier that interpolates the frequency response (interpolation frequency information) of the estimated subcarrier. In the present embodiment, the interpolation information generation unit 121 determines whether the FFT point (subcarrier number) is 3 among the FFT points (subcarriers) of the interpolation target band. Power to estimate the frequency response corresponding to the position of 85 or 386, 638, 639, etc. from the subcarrier where the signal actually exists (from the subcarrier of the signal band) As an example, extrapolate (interpolate) subcarrier number A case will be described in which the frequency response is outside the 385th subcarrier.

When calculating the frequency response from antenna 1, it is preferable that the sheath should also have the frequency response from antenna 1 at the sub-carrier position to be sheathed, as well as the frequency from antenna 2. In the case of calculating the response, it is preferable to extrapolate the frequency response from the antenna 2 at the subcarrier position to be enveloped. In the following example, the frequency response from antenna 1 is calculated and shown.

First, processing for estimating propagation path information from the transmitting antenna 1 will be described. In pilot complex conjugate signal generation section 108, the complex conjugate signal of known signal C C * = (cl X e " ^j

e " ^j ^{θ 1} , ········ c768 X e_j ^ei ) is generated. In the multiplication section 107, the first frequency information for each subcarrier is multiplied by the complex conjugate signal C * to obtain the second frequency information. Calculate

The actual frequency response on subcarrier k from transmitting antenna 1 is f, the transmitting antenna

1-k

Assuming that the actual frequency response from ナ 2 is f, the data input to extrapolation section 120 is ck =

2-k

Since ± 1 and dk = ± 1 are assumed, the operation on f can be calculated based on the frequency response from antenna 1

It depends on ck and dk whether it becomes a lath or minus, and it becomes plus if ck X dk = l and minus if ck X d k = 1. Here, since there is no need to limit particularly to θ 1 and Θ 2, assuming that Θ 1 = Θ 2 when transmitting, the frequency response input to extrapolation section 120 is f + f,

It becomes 1-k 2-k or f f.

1-k 2-k

[0057] In FIG. 2, for subcarriers in the signal band of FFT points 381 to 384, the 381st and 384th subcarrier forces Sf + f, 382 and 383th subcarriers according to the relation between ck and dk.

1-k 2-k

The case where f is f-f is shown. Second frequency of each calculated subcarrier

1-k 2-k

Information is input from the multiplication unit 107 to the interpolation information generation unit 121. The interpolation information generation unit 121 determines which of the subcarriers (FFT points) in the signal band is to be used to generate interpolation frequency information for interpolating the 385th subcarrier using the second frequency information.

First, an environment where the frequency variation of the propagation path is not so large in the entire signal band (frequency response of the propagation path The answer is assumed to be an almost constant environment). In this case, since it is considered that the variation in frequency response between subcarriers is small, the frequency response of the subcarrier to be interpolated is used using the frequency response of a small number of subcarriers within the signal band and as close as possible to the interpolation band. It is considered preferable to estimate the response. Here, the case of using frequency responses of the 383 and 384th subcarriers will be described. Let f — f, which is the second frequency information of the 383rd subcarrier, be f — f = F 383, and the 2nd of the 384th subcarrier

1-383 2- 383 1-383 2- 383

When f + f which is frequency information of f is f + f = F384, interpolation information

1-384 2-384 1— 384 2-384

The generation unit 121 calculates the value 385 of the 385th outlier as (F383 + F384) Z2,

1-385

Generate interpolation frequency information. Here, since the frequency variation is assumed to be constant at subcarrier positions 383 to 385, the frequency response from antenna 1 between these subcarrier positions and the frequency response from antenna 2 are regarded as almost identical. It becomes possible. By calculating (F383 + F384), only the frequency response from antenna 1 can be extracted. The subcarrier interpolation unit 122 interpolates the value calculated by the above calculation. When estimating the frequency response from the antenna 2, (F383−F384) / 2 is calculated and the same processing is performed.

The above method describes the case where ck X dk = ± 1 is limited to the following example. The following example describes a general case without limitation. The interpolation information generation unit 121 can use simultaneous equations as a method of estimating the propagation characteristics of force for each of the two antennas. For example, when transmitting characteristics from transmitting antenna 1 to H1, transmitting characteristics from transmitting antenna 2 to H 2, subcarrier 1 received signal to subcarrier 1, subcarrier 2 received signal to S2, transmitter antenna 1 to transmit Assuming that the code used in subcarrier 1 is C11, the code used in subcarrier 2 is C12, and the code used in transmission from transmit antenna 2 is C21 and C22, the received signal (SIS 2) is

[Number 1]

The propagation characteristics Hl and Η2 can be obtained by solving the simultaneous equations. This formula (1) In order for the simultaneous equations represented by to have a solution,

[Number 2]

(| r uc u ₂₁₎

(2)

, C ₂₂必要 need to be regular. In other words, it is necessary to select subcarrier 1 and subcarrier 2 in which equation (2) is regular.

That is, in order to calculate the frequency response from antenna 1 of subcarrier 385, antenna 1 (and 2) can be obtained by substituting the frequency response of subcarrier 383, 384 for the equation (1). The frequency response from can be calculated. The subcarrier interpolation unit 122 can improve the overall channel estimation accuracy by performing the same value interpolation as the frequency response of the subcarrier 385 by using the value calculated here. Also, in consideration of the frequency variation, the frequency response is calculated from the 381 and 382nd subcarriers, and the frequency response of the 385th subcarrier is calculated from the values previously calculated from the 383 and 384th subcarriers. It is also conceivable to use a method (such as a first order approximation).

The relationship between this determinant and the number of transmit antennas is at least M when the number of transmit antennas is M.

It is a necessary condition that a matrix of X M be generated and that the matrix be regular. In the present embodiment, since the number of transmitting antennas is two, the 2 × 2 row 歹 1J is shown as an example.

In an environment where there is not much frequency variation in the propagation path, interpolation information generation section 121 performs interpolation using the same value as the frequency response from each antenna calculated at the actual pilot subcarrier position (in equivalent interpolation). Although the case of generating frequency information has been described, the case of estimating frequency information of a subcarrier to be interpolated from a plurality of subcarriers in a signal band in consideration of fluctuation of frequency response will be described here. In this method, the frequency response of the combination of extrapolation bands from the frequency response of the subcarrier to which the pilot is actually transmitted (combination means the combination of the frequency responses of antenna 1 and antenna 2 power), etc. In this method, multiple patterns are calculated, and then the frequency response from each antenna at that subcarrier position is calculated from multiple patterns. Specifically, a case will be described where interpolated frequency information is generated using a value represented by the (1, Q) plane of the frequency response of each subcarrier. Figure 3 Fig. 3 shows the frequency response of subcarrier numbers 381 to 384 in Fig. 2 in the (1, Q) plane. Fig. 3 (a) shows subcarrier number 381, Fig. 3 (b) shows subcarrier number 382, Fig. 3 (c) is subcarrier number 383 and FIG. 3 (d) is subcarrier number 384. In FIG. 3, let the values in each I-Q plane be (X, Y) (k is a subcarrier number). For example, interpolation information kk

The module 121 performs the following procedure to estimate the 385th frequency response (to generate interpolated frequency information of the 385th subcarrier).

(11) Subcarrier group force with ckX dk = 1, etc. Estimate of subcarrier 385 frequency response (X 1, Y 2) when c 385 X d 385 = 1

385-1 385-1

(12) Estimation of subcarrier 385 frequency response (X 1, Y 2) in the case of c385 X d385 =-1 from the subcarrier group where ckX dk = _ 1.

385-2 385-2

(13) The above (11) and (12) power of 385th subcarrier frequency response (X, Υ

385 385

Calculated).

Assuming that there are two subcarrier groups used for estimation of the frequency response of synthesis of interpolation position, subcarriers 381 and 384 are used for (11). As an example, the interpolation information generation unit 121 obtains the following calculation result as the estimation method using linear interpolation in the form of phase plane.

As a result of (11), (X, Υ) is the subcarrier 381 frequency response (X,)) and

385-1 385-1 381 381 Since the frequency response (X, Υ) of subcarrier 381 is estimated to a first-order approximation,

384 384

It becomes 4 ΧΧ -X) / 3, (4 ΧΥ-)) / 3).

384 381 384 381

Similarly, when calculated from (12), (X, Υ) is ((3 ΧΧ − X), (3 (

It becomes 385-2 385-2 383 382 383))).

382

As (13), the value to be extrapolated as the 385th frequency response is ((X + Ζ) Ζ 2,

385-1 385-2

(Υ + Υ that is, ((4 ΧΧ + 9 ΧΧ-6 ΧΧ-X), (4 ΧΥ

385-1 385-2 384 383 382 381 3

+ 9ΧΥ -6ΧΥ-))).

84 383 382 381

As described above, according to the present embodiment, when transmitting symbols transmitted by modulating each subcarrier with different known signals in each of a plurality of antennas, subcarriers of the same subcarrier number are used. By selecting the frequency information of the subcarrier to interpolate based on the combination of the modulated known signals, received from multiple antennas Frequency information to be interpolated can be calculated using frequency information of subcarriers selected in accordance with the characteristics of the carrier. This makes it possible to reduce distortion that occurs in the time despreading channel estimation method.

In the present embodiment, only two antennas are dealt with, but the number of antennas can be extended to three or more by the same method.

Also, although transmission antenna 1 has been described above, when calculating the frequency response of the multicarrier symbol transmitted from transmission antenna 2, pilot complex conjugate generation section 108 generates a complex conjugate signal of Dk as a code. The frequency response from the transmitting antenna 2 can be calculated by generating and performing an outer ring 120 in the same manner.

Furthermore, in the present embodiment, an example of two estimation methods of equivalent interpolation and linear linear interpolation has been described, but various estimation methods other than those described above can be considered, and these should be applied. Is also possible.

Second Embodiment

In the second embodiment, a case will be described where the transmitter side generates a channel estimation OFDM symbol using the CI method. The configuration of the receiver 100 is the same as that of FIG. In the CI method, a propagation path estimation symbol is generated, for example, by a code C, and further, a force generated by giving a constant phase rotation between subcarriers, by setting the phase rotation amount to a different value between antennas, the receiver Identification 'in method of enabling propagation channel estimation. Here, this phase rotation amount is also regarded as a part of the code, and it is considered that an OFDM signal for channel estimation is generated with a different code at each transmitting antenna.

Therefore, when the CI method is used, the known signal C and the known signal D in the first embodiment have a specific relationship as a known signal for generating an OFDM symbol for channel estimation used in each antenna. It points to the case. The specific relationship is a code that the known signal D is generated from the known signal C, and when assigning the known signal C to a subcarrier, a code that is generated by applying a constant phase rotation between successive subcarriers. Is pointing to the case. In the present embodiment, assuming that the phase rotation amount is π, ck and dk are

[Number 3] It is assumed that dk = ck xe ^{J 7r x (k mod 2} ( ₃ ) (where j Xj =-1), that is, the known signal used in antenna 1 has 0 between the subcarriers with respect to code C. The known signal used in the antenna 2 is given a phase rotation amount of π between subcarriers with respect to the code C.

Here, a propagation path estimation technique using the CI method will be described. In the following, for simplicity of explanation, we will use 2 transmitting antennas (1 transmitting antenna, 2 transmitting antenna). In addition, it is assumed that all subcarriers in the propagation path estimation OFDM symbol are used as pilot subcarriers for propagation path estimation and are known among the transceivers.

From transmit antenna 1, as components for propagation path estimation, component ck (k is a positive integer within the number of subcarriers) of known signal C is assigned to all subcarriers between the transmitter and receiver, Generate and transmit OFDM symbols for channel estimation.

Similarly, from transmitting antenna 2, as a channel estimation OFDM symbol, component dk of known signal D is allocated to all subcarriers between the transmitter and the receiver, and a channel estimation FF DM symbol is generated. To send. However, ck and dk are related as shown in the above equation (3), and dk is a code generated by converting the signal of ck according to a specific rule.

Next, a schematic operation in the case where the propagation channel estimation OFDM symbol generated by the CI method is received and propagation channel estimation section 201 estimates a propagation channel will be described.

FIG. 4 shows an example of the waveform of the output of IFFT section 109 of receiver 100. The total number of paths in the propagation path from transmitting antenna 1 to the receiving antenna is 3 (each delay power Stl, t2 and t3), and the total number of multipaths from transmitting antenna 2 to the propagation path of the receiving antenna is 4 (each delay is t 1 , T2, t3, and t4) show waveforms of the IFFT unit 109, where tl to t4 are integral multiples of the time resolution of IFF T. In FIG. 4, the horizontal axis indicates the point of IFFT (corresponding to the time of the delay profile), and the vertical axis indicates the power. Fig. 4 (a) shows the case where the signal generated by the pilot complex conjugate signal generation unit 108 is a ck complex conjugate signal, and Fig. 4 (b) shows this signal as a dk complex conjugate signal. The situation is shown in Fig. 4 (a), where the pulse generation position is replaced. When the total number of IFFT points is N, the difference between the path from transmit antenna 1 and the path from transmit antenna 2 is observed at a position separated by N / 2 points. This is because dk is set to ck and the amount of phase rotation between adjacent subcarriers is set to π (see equation (3)). Therefore, when calculating the propagation path from the transmitting antenna 1, the noise removing unit 110 removes the pulse corresponding to the signal power from the transmitting antenna 2, and the frequency conversion is performed by the FFT unit 111, whereby the transmitting antenna 1 is obtained. It is possible to calculate the frequency response from Similarly, in the case of calculating the propagation path from the transmission antenna 2, the noise removing unit 110 removes the pulse corresponding to the signal power of the transmitting antenna 1 power, and frequency conversion is performed by the FFT unit 111. It is possible to calculate the frequency response from

By changing the amount of phase rotation shown here, the process can be similarly performed even with three or more transmitting antennas. For example, in the case of using four antennas, it is possible to calculate four types of imperorence responses by setting the phase rotation amount between subcarriers with respect to the component ck to be 0, π / 2, π, 3πΖ2. It becomes possible. However, it is necessary to design in such a range that it does not overlap with the delay waves due to each multipath and other imprintless groups.

Next, details of the operation of the extrapolation unit 120 of the present embodiment will be described. In the present embodiment, the interpolation information generation unit 121 generates interpolation frequency information using the second frequency information of the subcarrier selected based on the phase difference given to the known signal. FIG. 5 is an example of a waveform (second frequency information) input to the mantle 120 in the present embodiment. The difference from FIG. 2 is that in the first embodiment, since the code is not relevant, the sub

1-k 2-k carrier and subcarrier which becomes f-f is code combination (combination of ck and dk

1-k 2-k

However, in the present embodiment, since ck and dk have a relationship as shown in equation (3), f + f and f − f force are to be repeated every Si subcarrier. .

1-k 2-k 1 -k 2-k

Therefore, when estimating the frequency response of the guard band position subcarrier in the outer ring unit 120, if the subcarrier number is even, estimation is performed from the actually received even subcarrier. In the case of an odd number, estimation is performed from an odd number of subcarriers. The following shows an example of the case where two subcarriers (385 and 386th subcarriers) are covered by the mantle part 120.

[0079] In the case where there is almost no frequency variation of the propagation path in a certain frequency band In sub-carriers near the rear, when there is little propagation path fluctuation), the interpolation information generator 1 21 ί, 385 サブ subcarrier サブ 383 値 386 直直同同Interpolation should be done. In the first embodiment, the extrapolation processing is performed for each antenna, and when calculating the frequency response from the transmitting antenna 1, a method is adopted in which the frequency response of the transmitting antenna 1 is extrapolated. The need is to surpass the synthetic frequency response from all antennas. The reason is briefly described.

[0080] The purpose of the outer ring is to prevent the frequency response distortion due to the spread of signal power when obtaining the time response in the time despreading channel estimation method when the number of subcarriers and the number of FFT points are different. . In the first embodiment, in the case of estimation similar to the second embodiment, there is a trade-off between reduction of distortion due to extrapolation and increase in distortion due to deterioration of accuracy due to increase in interference component. It becomes a relationship. Therefore, when obtaining the frequency response from the transmitting antenna 1 so as not to increase the interference component, the estimated value of only the frequency response with the transmitting antenna 1 is extrapolated.

On the other hand, in the present embodiment, since dk is a code generated from ck according to equation (3), the signal can be separated at the output of the IF FT unit. Furthermore, when the envelope as shown in this embodiment is performed, the signal component from the antenna for which the frequency response is calculated and the signal component of the antenna power as interference also contribute to the reduction of the spread in the time response. There is almost no increase in Therefore, in the present embodiment, the extrapolation means as described above is used.

Next, the case where the frequency variation of the propagation path in the frequency band is moderate will be described. In this case, the accuracy can be improved by estimating the frequency response of the subcarrier to be interpolated by means such as linear interpolation from a plurality of subcarriers in the signal band. In this embodiment, a method of performing linear interpolation from two actually received subcarriers is shown. In the case of performing the outer guard on the odd-numbered subcarriers, in the case of performing the outer guard on the even-numbered subcarriers from the received odd-numbered subcarriers, it is estimated from the received even-numbered subcarriers It will be outcast.

FIG. 6 is a diagram for explaining an example of selection of subcarriers to be interpolated. In FIG. 6, H ^P is

Q

The frequency response for the Qth subcarrier (FFT point) is shown for the known signal transmitted from antenna P. R is the received signal of the Qth subcarrier and In this figure, the signal band (subcarriers from k-5 to k) is the signal actually received, and to the extrapolation section 120 outside the signal band (subcarriers after k + 1). This is an extrapolated signal. Subcarrier k is at the end of the signal band. When extrapolating, the information calculated using the frequency response of k_ 1 and k_3 is used for subcarrier number k + 1, and the frequency response of k and k−2 is used for k + 2. It is shown that the information calculated by the above calculation is interpolated, and the interpolation is similarly performed for k + 3 and thereafter. The relationship between the position to be interpolated and the subcarrier position for generating information to be interpolated is unique by the number of antennas used and the amount of phase rotation when generating an OFDM symbol for channel estimation using the CI method, which will be described in detail later. It is possible to set it to S. As shown in FIG. 6, when two antennas and the phase rotation amount is π, the signal from the transmitting antenna 2 is inverted every other subcarrier. Therefore, the interpolation information generation unit 121 generates interpolation frequency information using the frequency response of every other subcarrier. Also, the calculation of the frequency response of synthesis at the subcarrier position to be excluded is the same as the case shown by equivalence interpolation.

Here, linear interpolation of the first order is shown as an example. Specifically, the method of extrapolating to the 385th subcarrier position and the 386th subcarrier position is shown. Fig. 7 shows the frequency response of subcarrier numbers 381 to 384 in Fig. 5 in the (1, Q) plane. Fig. 7 (a) shows subcarrier numbers 381 and Fig. 7 (b) shows subcarrier numbers. 382, FIG. 7 (c) is subcarrier number 383, and FIG. 7 (d) is subcarrier number 384. In Fig. 7, let (X, Y) be the values in each I-Q plane. For example, the interpolation information generation unit 121 estimates the 385th frequency response k k

In order to do this, follow the steps below.

(21) 381, the 383rd subcarrier group force and so on estimate the 385th.

(22) 382, 384th subcarrier group power 386th estimated.

[0085] Compared to the first embodiment, there is no third step, but as described above, impulses are separated after IFFT without estimating the propagation path from each antenna at the outer cover position. Therefore, it is possible to improve the channel estimation characteristics in the band in the first two steps (just by calculating the synthesized frequency response).

[0086] In this way, from (21) above, (X 1, Y 2) are used for (Χ, Υ) and (X,))

385 385 381 381 383 383 ((2 Χ — X), (2 Υ Υ — Υ)). Similarly, the above (22) to (X, Y) are ((2 Χ Χ-X), (2 Υ Υ-))) and

386 386 384 382 384 382

[0087] In the present embodiment, two estimation methods, ie, equivalence interpolation and linear linear interpolation, have been described, but various estimation methods other than the two can be used. It is important to determine the subcarriers to use for estimation based on the rotational phase according to the CI method and the number of transmit antennas when calculating the frequency response to be excluded.

Another method of estimation is to follow only the phase. This means that when interpolating odd subcarriers after the 385th, the amplitude is the same as the 383th, the difference between the 381st phase and the 383th phase is the same as the 383th and 385th phase differences, and , Is a method to do the same process.

In addition, the number of lines to be interpolated is preferably large if the delay dispersion of the propagation path is small, and good characteristics can be obtained.

Furthermore, as shown in the second embodiment, when one code is used as a reference, another code is generated by giving a phase rotation, and a known signal of a channel estimation OFDM signal is generated. It is as follows when generalizing how to select the subcarrier which is the source of the frequency information to interpolate. When the phase rotation amount Θ of each antenna can be represented by an integral multiple of Θ g, the subcarrier group used to perform the covering can be determined as follows. First, m X I θ I = 2η π (m, n is a natural number, | θ | is the absolute value of Θ)

g

Let Lm be the smallest m (LCM-A is a natural number). Assuming that the subcarrier number of the position to be extrapolated is k, the received subcarrier at a position distant by a multiple of LCM-A from k may be used as the subcarrier used to perform the extrapolation. That is, the interpolation information generation unit 121 selects frequency information for the medium power of subcarrier kLCM_A, k ± 2LCM_A, which is disposed apart from LCM_A starting from subcarrier k to be interpolated, and subcarrier k Estimate the frequency response of

Further, in order to generalize the amount of phase rotation, a difference 差 between the amounts of phase rotation given between the respective antennas is required. Therefore, assuming that the number of antennas used is M, M X (M−D / 2 diff

It is necessary to use different types of phase rotation differences.

[0092] For all phase rotation amount differences m, m XI θ I = 2η π (a, diff is MX (M l) Calculate the smallest m that satisfies / 2 or less and all integers). Then, let LCM-B be the aa least common multiple of all m, then LCM-B means the repetition of the waveform. That is, the interpolation information generation unit 121 uses LCM starting from the subcarrier k to be interpolated.

The frequency information is selected from among subcarrier k soil LCM_B, k ± 2 LCM_B, which are arranged at multiples of _B, and the frequency response of subcarrier k is estimated. However, considering fluctuations in the frequency response, it is better to use a subcarrier close to the subcarrier that performs the outer ring as much as possible.

By performing the envelope as described above, accurate channel estimation can be performed using the channel estimation OFDM symbol transmitted by the CI method.

In each of the above embodiments, the first embodiment shows one example as an example of the number of extras, and the second embodiment shows two examples as the number of extras. The meaning depends on the propagation path environment in which the naive system is used. Also, when performing subcarrier interpolation even when power is inserted at regular intervals, which indicates that all subcarriers as OFDM symbols for channel estimation are used as pilot carriers, the intervals are taken into consideration. It is possible to estimate the propagation path with high accuracy as well.

Brief description of the drawings

FIG. 1 is a block diagram showing an example of the configuration of a multicarrier wireless receiver according to the present invention.

FIG. 2 is a view showing an example of an input waveform to the mantle according to the first embodiment.

FIG. 3 is a diagram showing frequency responses of subcarrier numbers 381 to 384 in FIG. 2 in the (1, Q) plane.

FIG. 4 is a diagram showing an example of the waveform of the output of the IFFT unit of the receiver.

FIG. 5 is a diagram showing an example of an input waveform to the mantle in the second embodiment.

FIG. 6 is a diagram for explaining selection of subcarriers to be interpolated.

FIG. 7 is a diagram showing frequency responses of subcarrier numbers 381 to 384 in FIG. 5 in the (1, Q) plane.

Explanation of sign

[0096] 100 receivers 101 antenna unit

102 wireless receiver

103 A / D converter

104 OFDM Symbol Synchronizer

105, 111 FFT unit

106 pilot extractor

107 multiplication unit

108 Pilot complex conjugate signal generator

109 IFFT unit

110 Noise removal unit

112 Channel compensation unit

113 Decoding unit

120 Extrapolation

Interpolation information generator

122 Subcarrier Interpolation Unit

201 Channel estimation unit

Claims

The scope of the claims

[1] A receiver for receiving propagation path estimation symbols transmitted from a plurality of transmit antennas, including subcarriers modulated with different known signals, and estimating the propagation paths from the respective transmit antennas,

A Fourier transform unit that Fourier-transforms the received channel estimation symbol and calculates first frequency information for each subcarrier;

A signal generation unit that generates a known signal used to modulate subcarriers included in the propagation path estimation symbol;

A division unit that divides the first frequency information by one of the known signals to calculate second frequency information;

Extrapolation unit for calculating information of frequency response from the transmitting antenna at a position where no subcarrier is transmitted from the first frequency information or the second frequency information · Interpolation to calculate third frequency information When,

A receiver comprising: an inverse Fourier transform unit configured to perform an inverse Fourier transform on the third frequency information.

[2] The outer ring section selects subcarriers based on a combination of known signals obtained by modulating subcarriers at the same position of propagation path estimation symbols transmitted from the plurality of antennas, and selects the selected subcarrier. The receiver according to claim 1, further comprising an interpolation information generation unit that generates frequency information to be interpolated using frequency information.

[3] The receiver according to claim 2, wherein the interpolation information generation unit selects a subcarrier in which a matrix generated by a known signal different for each of the plurality of antennas is regular.

[4] A plurality of transmit antennas including transmit- ted antennas including subcarriers modulated with different known signals generated by providing different phase rotation amounts 毎 for each transmit antenna between each element of a predetermined code, and transmission propagation A receiver for receiving path estimation symbols and estimating a propagation path from each of the transmit antennas;

A Fourier transform unit that performs Fourier transform on the received channel estimation symbol to calculate first frequency information for each subcarrier; A signal generation unit that generates a known signal used to modulate subcarriers included in the propagation path estimation symbol;

An outer portion configured to calculate information of the frequency response synthesized at the position where the subcarrier is not transmitted based on the phase rotation amount from the second frequency information, and generate third frequency information. ,

[5] The mantle calculates the difference Θ for all two different Θ, based on Θ

diff diff

5. The receiver according to claim 4, further comprising: an interpolation information generation unit that selects subcarriers and generates frequency information to interpolate frequency information of the selected subcarriers.

[6] The interpolation information generation unit is configured to set the m x θ for each phase rotation amount difference Θ.

diff I diff I = 2 η π (m, η is a natural number, I θ I is an absolute value of)) Calculate the smallest m that satisfies and calculate the least common multiple of m LCM-B (LCM-B is an integer 6. The reception method according to claim 5, wherein frequency information is selected from among the subcarriers arranged apart from the least common multiple LCM-B with the subcarrier to be interpolated as a starting point. Machine.

[7] The extrapolation section may be configured such that m X I Θ g if all of the phase rotation amounts Θ are integer multiples of Θ g.

The minimum m that satisfies I = 2ηπ (m, n is a natural number and | θ | is the absolute value of LC) LCM_A (

The LCM-A is calculated as an integer), and frequency information is selected from among the subcarriers arranged apart from the least common multiple LCM_A starting from the subcarrier to be interpolated. Receiving machine.

[8] The receiver according to claim 1 or 4, wherein the interpolation information generation unit selects frequency information of a subcarrier close to a subcarrier to be interpolated.

[9] A method of estimating frequency information including subcarriers modulated with different known signals, receiving propagation path estimation symbols transmitted from a plurality of transmission antennas, and estimating propagation paths from the respective transmission antennas And Fourier transform the received channel estimation symbol to calculate first frequency information for each subcarrier;

Second frequency information is calculated by dividing the first frequency information by one of known signals used for modulation of subcarriers included in a channel estimation symbol;

From the first frequency information or the second frequency information, information of frequency response from the transmitting antenna at a position where no subcarrier is transmitted is calculated and interpolated to calculate third frequency information.

A frequency information estimation method characterized by performing inverse Fourier transform on the third frequency information.

A plurality of transmit antennas including subcarriers modulated with different known signals generated by giving different amounts of phase rotation 毎 to each transmit antenna between elements of a predetermined code, and for transmitting channel estimation. A frequency information estimation method for receiving symbols and for estimating a propagation path from each of the transmit antennas,

Fourier-transform the received channel estimation symbol to calculate first frequency information for each subcarrier;

From the second frequency information, information of frequency response synthesized at a position where no subcarrier is transmitted is calculated based on the phase rotation amount · interpolation is performed to generate third frequency information.